在 PostgreSQL 的 WHERE 子句中使用函数结果

Question

我尝试在

where

子句中使用函数执行的结果，但没有成功：

SELECT clinics.*, distance_between_objects(1, id, 7, 3) AS dist FROM clinics WHERE dist<=1;

给我：

Column "dist" does not exists

。 引用它就像：

SELECT clinics.*, distance_between_objects(1, id, 7, 3) AS dist FROM clinics WHERE "dist"<=1;

也没有帮助。请告知Postgres是否有可能在WHERE子句中使用函数结果而不调用它两次？ 谢谢！

Answer 1

避免拨打

distance_between_objects

两次：

--Subquery
SELECT * FROM (
    SELECT 
        *, 
        distance_between_objects(1, id, 7, 3) AS dist 
    FROM 
        clinics) AS clinics_dist 
WHERE 
    dist <= 1;

--CTE
WITH clinics_dist AS (
    SELECT 
        *, 
        distance_between_objects(1, id, 7, 3) AS dist 
    FROM 
        clinics
)
SELECT 
    * 
FROM 
    clinics_dist 
WHERE 
    dist <= 1;

在我看来，

CTE

是一种更干净的方法。

Answer 2

您也可以使用横向

SELECT *
FROM clinics,
LATERAL (SELECT distance_between_objects(1, id, 7, 3) AS dist) l
WHERE l.dist <= 1;

Answer 3

以前从未见过横向。我一定要尝试一下！

Answer 4

您可以在where子句中使用该函数：

SELECT clinics.*, distance_between_objects(1, id, 7, 3) AS dist 
FROM clinics 
WHERE distance_between_objects(1, id, 7, 3)<=1;